1. Field of the Invention
The present invention relates to an illumination apparatus for illuminating a liquid crystal monitor and a digital camera having a liquid crystal monitor using the LC illuminating apparatus.
2. Description of the Prior Art
In general, in known digital cameras, a liquid crystal monitor (LC monitor) is used to view an object and an image of the object taken by the camera. To enable a viewer to view the LC monitor even in poor light, or in a dark place, a backlight is provided in the camera.
The backlight is configured to allow light, emitted from a fluorescent lamp incident upon the LC monitor through a light guide and a reflecting plate, to illuminate the surface of the LC monitor. In case of a fluorescent lamp that is a cold-cathode fluorescent lamp, an AC lamp lighting circuit, whose service life is 10000 hours on an average, is usually employed.
However, if the LC monitor is illuminated by a backlight having a fluorescent lamp which is lit by the AC lighting circuit, the image displayed on the LC monitor tends to be unclear due to noise caused by an invertor of the AC lighting circuit, thus resulting in a lower image quality than the image displayed on an LC monitor using a DC lighting circuit. To prevent this, it is theoretically possible to light the fluorescent lamp by a DC lighting circuit instead of the AC lighting circuit, so that the noise caused by the invertor can be reduced to thereby enhance the image quality. However, in the fluorescent lamp activated by the DC lighting circuit, a blackening phenomenon tends to occur within a shorter time span than in the fluorescent lamp activated by the AC lighting circuit. Consequently, the service life of the LC monitor is shortened.
It is an object of the present invention to provide a liquid crystal monitor illuminating apparatus wherein if the fluorescent lamp is activated by a DC lighting circuit to obtain a clear display of the LC monitor in which a noise caused by an invertor is restricted, a blackening phenomenon of the fluorescent lamp tends not to occur, thus resulting in an prolonged service life of the LC monitor.
Another object of the present invention is to provide a digital camera having a liquid crystal monitor using the LC monitor illuminating apparatus.
In order to achieve the above-mentioned objects, there is provided a liquid crystal monitor illuminating apparatus in which a fluorescent lamp provided in a backlight portion to illuminate a liquid crystal monitor from behind including: a direct-current lighting circuit which activates the fluorescent lamp; and a switching circuit which reverses the polarity of the direct-current lighting circuit.
Preferably, the switching circuit reverses the polarity of the direct-current lighting circuit every time the fluorescent lamp is activated.
Preferably, the switching circuit reverses the polarity of the DC lighting circuit every time a main switch, provided on a main body which sends indication data to the LC monitor, is turned ON.
Preferably, the switching circuit reverses the polarity of the DC lighting circuit at a predetermined time interval.
Preferably, the predetermined time interval is determined by a CPU, in accordance with a lapse time which is measured by measuring clock pulses which are generated by a clock generator which sends indication data to the LC monitor.
Preferably, the liquid crystal monitor illuminating apparatus is provided in a digital camera.
The present disclosure relates to subject matter contained in Japanese Patent Application No.10-230693 (filed on Aug. 17, 1998) which is expressly incorporated herein by reference in its entirety.